Tighter query for images.

Use a more-precise selector query for <img> tags within figures, better
matching the Parsoid DOM spec.

Change-Id: I7d42eaa8ec02d4a1066e9344a18f2263e2efbfd4
Use default papersize when bundling.

We use the de facto convention established by `libpaper` on linux.
On other platforms, `/etc/papersize` probably doesn't exist, and so
we don't specify a papersize in the metabook.

An explicit papersize in the metabook json overrides the default.

Bug: 68836
Change-Id: If9657503522a95fc3c30867c71526415a3bc9d15
Merge "Tighter query for images."